1. Field of the Invention
This invention relates to a method and apparatus for measuring the force applied to a seat belt. Specifically, a sensor arrangement is mounted on a rigid plate secured between a seatbelt portion and a vehicle structure and includes a guide member for guiding the seatbelt portion to isolate the sensor from input forces applied at an angle to the seatbelt portion, which increases the accuracy of the seatbelt force measurements.
2. Related Art
Most vehicles include airbags and seatbelt restraint systems that work together to protect the driver and passengers from experiencing serious injuries due to high-speed collisions. It is important to control the deployment force of the airbags based on the size of the driver or the passenger. When an adult is seated on the vehicle seat, the airbag should be deployed in a normal manner. If there is an infant seat or small adult/child secured to the vehicle seat then the airbag should not be deployed or should be deployed at a significantly lower deployment force. One way to control the airbag deployment is to monitor the weight of the seat occupant.
Current systems for measuring the weight of a seat occupant are complex and expensive. One type of system uses pressure sensitive foil mats mounted within the seat bottom foam. Another system uses sensors placed at a plurality of locations within the seat bottom. The combined output from the mats or the sensors is used to determine the weight of the seat occupant. The accuracy of the weight measurements from these types of sensor systems can be compromised due to additional seat forces resulting from the occupant being secured to the seat with a seatbelt.
For example, weight sensor systems can have difficulty identifying an adult, a child, or a car seat when the seatbelt is being used. When a child seat is secured to a seat with a seatbelt, an excess force acts on the sensors mounted within the rear portion of the seat bottom, which interferes with accurate weight sensing. Over tightening of the seatbelt to securely hold the child seat in place, pulls the child seat down against the rear part of the seat bottom, causing the excessive force measured by the sensors. Due to this effect, the current weight sensing systems have difficulty in discerning between an adult belted to a seat and a child seat secured to the seat with a seatbelt.
In order to address this problem, sensors have been incorporated into the seatbelt to measure the tension force applied to the seatbelt as passengers or a child seat is secured to the seat. High seatbelt tension forces indicate that a child seat is secured to the seat. One type of seatbelt force sensor is mounted on a rigid plate member having one end attached to a seatbelt portion. The sensor measures strain applied to the plate via the seatbelt. This type of sensor provides accurate measurements for input loads that are applied linear or axial direction. However, if the seatbelt is pulled or tightened at an undesirable angle, the sensor can provide less accurate measurements.
Thus, it is desirable to have a system for measuring seatbelt forces to determine whether a child seat or an adult is secured to the seat that utilizes a sensor that is isolated from non-axial movements, and which provides increased accuracy for seatbelt force measurements. The system should also work with traditional seat occupant weight sensing systems and be easy to install, as well as overcoming any other of the above referenced deficiencies with prior art systems.
A system for measuring seatbelt forces includes a rigid plate member that supports a seatbelt force sensor and a guide member for isolating the sensor from input forces applied to the seatbelt at undesirable angles. The method of measuring the seatbelt force includes the following steps. One end of the rigid plate member is mounted to a seatbelt portion and an opposite end of the rigid plate member is mounted to a vehicle structure. An input force is applied to the seatbelt portion. The seatbelt portion is guided by a guide member to isolate the seatbelt force sensor from input forces applied at an angle. The seatbelt force sensor generates an output signal that is representative of the force applied to the seatbelt portion. Preferably, the guide member is pivotally mounted at one end between the rigid plate member and the vehicle structure.
In a disclosed embodiment of this invention, the sensor assembly includes a rigid member having one end operably coupled to a seatbelt portion and a sensor mounted on the rigid member for measuring strain exerted on the rigid member by an input force applied to the seatbelt portion. The assembly further includes a bracket having a first mounting portion for attachment to the rigid member and a second mounting portion for attachment to a vehicle structure, such as a B-pillar, anchor side mount, or buckle side mount. This bracket defines a guide for isolating the sensor from non-axial input forces applied to the seatbelt portion. Preferably the first mounting portion is parallel to the rigid member and the second mounting portion is transverse to the rigid member.
In a disclosed embodiment, the second mounting portion includes a pair of bosses mounted on opposing sides of the bracket. Each of the bosses includes an aperture for supporting a pivot shaft. The bracket pivots about a pivot axis defined by the pivot shaft and relative to the vehicle structure. This configuration provides a guide for the seatbelt to eliminate angle effects on the sensor.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.